1. Field of the Invention
The present invention relates to contact type temperature measuring apparatuses which measure the temperature of a substrate (hereinafter referred to as a "wafer") undergoing the heat treatment, when various heat treatments are applied to various kinds of wafers, such as a semiconductor wafer, by a heat treatment apparatus such as a light irradiation heating apparatus (a lamp annealer), a sputtering apparatus, a CVD (Chemical Vapor Deposition) apparatus and an epitaxial growth apparatus. In particular, the present invention relates to technology with which, in an apparatus which measures the temperature of a wafer by making a temperature sensing element in contact therewith, contact between the wafer and the temperature sensing element can be easily sensed.
2. Description of the Related Art
When a semiconductor device or the like is manufactured by applying various kinds of heat treatments to a wafer in a heating furnace or the like by various kinds of heat treatment apparatuses, it is essential to accurately measure the temperature of the wafer under heat treatment. Methods of measuring the temperature of a wafer are divided into a contact type and a non-contact type. In the contact type method, the temperature of a wafer is measured by making a temperature sensing element of a temperature sensor directly in contact with the wafer. In the non-contact type method, the temperature of a wafer is measured by sensing energy radiated from the surface of the wafer using an infrared radiation thermometer. A contact type wafer temperature measuring apparatus is disclosed in Japanese Patent Laying-Open No. 4-148545, which is a counterpart application of U.S. Ser. No. 07/774,943 now U.S. Pat. No. 5,315,092 in which a part of a temperature sensing element is formed into a flat surface, which supports a part of a wafer, thus making the temperature sensing element in surface contact with the wafer. The structure of the apparatus which measures the temperature of a wafer will be described hereinafter in detail with reference to FIGS. 1 to 3.
FIG. 1 shows one example of a heat treatment apparatus which includes a temperature measuring apparatus of a wafer. In this example, the apparatus is of a light irradiation type. FIG. 1 is a front view of a main portion showing in cross section a part of a schematic structure of the heat treatment apparatus. FIG. 2 is a plan view showing a temperature sensing element of the temperature measuring apparatus, together with a part of a wafer holder (susceptor) of the apparatus shown in FIG. 1 and a wafer. FIG. 3 is a perspective view for explaining a state where a part of the wafer is supported by the temperature sensing element of the temperature measuring apparatus. It should be noted that the temperature sensing element is not shown in FIG. 1, and that the susceptor is not shown in FIG. 3.
Referring to FIG. 1, a schematic structure of a light irradiation type heat treatment apparatus is first described in the following. In the figure, a heating furnace 40 has an opening for insertion and removal of a wafer, and is formed of quartz glass which transmits infrared light. A front chamber 44 formed in a tubular shape is provided in contact with opening 42 of heating furnace 40. A lid 46 is provided so as to close a front end opening surface of front chamber 44. A resin packing 48 is attached to a surface of front chamber 44 abutting lid 46, for hermetically sealing heating furnace 40 when heating furnace 40 is sealed by lid 46. A plurality of light sources 50 for irradiating light, such as a halogen lamp or a xenon arc lamp, are disposed above and under heating furnace 40, opposing an upper wall surface and a lower wall surface of heating furnace 40, respectively. At the back of light sources 50, reflectors 52 are provided.
A susceptor 54 formed of quartz is fixed to an inner surface of lid 46. Susceptor 54 has a wafer supporting portion 56, on which a wafer 10 is mounted and supported. An outer surface of lid 46 is fixed to a support block 58. By moving support block 58 linearly in the direction of an arrow by a driving mechanism, not shown, lid 46 is opened/closed. At the same time, wafer 10 is carried in and out from heating furnace 40 through opening 42. When a plurality of wafers are subjected to heat treatment one by one, wafer 10 after treated is carried out from heating furnace 40and removed from susceptor 54 by a feed arm, not shown. Then, a wafer to be treated next is mounted onto susceptor 54 by the feed arm. The wafer to be treated next is again carried into heating furnace 40 for the next heat treatment operation.
As shown in FIG. 2, wafer 10 is supported horizontally at three points by two projecting supporting portions 62, 62 formed projecting from an annular portion 60 at the tip of susceptor 54 of quartz, and a tip portion of a temperature sensing element 64 of the temperature measuring apparatus. Susceptor 54 and temperature sensing element 64 are fixed at a portion, not shown, to be horizontally held. Temperature sensing element 64 includes, for example, a sheathed thermocouple, and a capillary coating member coating the entire sheathed thermocouple. The coating member is formed of SiC (silicon carbide) of high purity manufactured with, for example, a CVD method. Since such a coating member is highly heat resistant, has high thermal conductivity, and is formed into a thin capillary shape, the coating member has an extremely small heat capacity as compared to wafer 10. In addition, since the coating member does not include impurity which might cause contamination of the surface of wafer 10, the coating member will not contaminate wafer 10. The sheathed thermocouple, with a sheathed portion of an outer diameter of approximately 0.3 mm and a length of approximately 200 mm, for example, is inserted deep into the capillary coating member to the vicinity of the tip.
As shown in FIG. 3, the coating member is formed in a shape of a long thin annular tube with the tip clogged. The coating member has an outer diameter of approximately 0.8 mm, an inner diameter of 0.4 mm, and a length of approximately 200 mm, for example. The tip portion of the coating member is processed into a flat surface 66 of a width of approximately 0.5 mm and a length of approximately 15 mm, for example. Temperature sensing element 64 is disposed so as to be in surface contact with wafer 10 at flat surface 66 of its tip portion.
Temperature sensing element 64 having the above-described structure supports wafer 10 with flat surface 66 at its tip portion over approximately 10 mm from its tip, and is kept in contact with wafer 10. During heat treatment of wafer 10 by the light irradiation type heat treatment apparatus as shown in FIG. 1, when the surface temperature of wafer 10 increases, the coating member of temperature sensing element 64 is also heated by thermal conduction. The coating member of temperature sensing element 64 has very high thermal conductivity because of a substantially smaller heat capacity as compared to wafer 10 and surface contact with wafer 10. Therefore, the coating member of temperature sensing element 64 is heated by thermal conduction to quickly attain the same temperature as that of wafer 10. The sheathed thermocouple inserted into the vicinity of the tip of the coating member can measure the temperature of the tip portion of the coating member accurately.
When the temperature of the wafer is measured by the temperature sensing element of the temperature measuring apparatus directly in contact with the wafer as described above, the temperature measuring accuracy largely depends on a state of contact between the temperature sensing element and the wafer. Failure in mounting of the wafer on the susceptor, deterioration of a wafer in shape, such as curvature, and poor setting of the susceptor or the temperature sensing element might cause poor contact between the temperature sensing element and the wafer, resulting in failure of accurate measurement of temperature of the wafer. Therefore, it is necessary to check contact between the wafer and the temperature sensing element.
It has conventionally been determined whether the state of contact is appropriate or not based on visual check and observation of a treated wafer. More specifically, after it is visually confirmed that the temperature sensing element and the wafer are in contact with each other appropriately, heat treatment is actually applied to the wafer. After heat treatment, the wafer is tested. Based on the test result, it is determined whether or not the wafer is heat-treated at a target temperature. It has been thus recognized conventionally that the state of contact was appropriate.
However, in the manufacturing process of a semiconductor device, for example, if wafers are heat-treated while being checked one by one as described above, productivity is considerably lowered. In order to avoid reduction of productivity, it is possible to carry out the above-described checking once each time hundreds or thousands of wafers are heat-treated. However, in this case, it is not possible to check deterioration of the state of contact between the temperature sensing element and the wafer which might occur for some reason during a series of heat treatments. There is a possibility that unfavorable heat treatment might be continued until the next checking operation is carried out, thus reducing the yield.